The present invention relates to a process for mounting an optical fiber in a connector element, and more precisely, a connector element of the type intended to be assembled in a joining element, opposite an identical connector element, to provide for the connection of two immobilized optical fibers, each in one of the connector elements.
The connector element for carrying out the process according to the invention is of the type comprising a peripheral joining nut; a body, whose front end surface defines a reference plane, provided at its rear end with means to retain an optical fiber introduced into the rear end of said body; a ferrule in which the stripped end of the optical fiber can be positioned, which is accommodated in said body and projects axially toward the front of the same, the front end face of said ferrule being located at a predetermined axial distance from said plane of reference.
In such connector elements, the reference distance, that is the above-mentioned distance between the front face of the ferrule and the plane of reference defined by the front end surface of the body, must be observed with precision, because it is standardized.
The stripped end of the optical fiber must either be located in the plane of the end face of the ferrule, or preferably be recessed by a predetermined distance, for example 20 microns, with respect to this end surface.
The technique currently utilized, to assure coincidence between the stripped end of the optical fiber and the end face of the ferrule of the connector element, consists of adhering the stripped fiber in the axial hole of the ferrule, into which it is introduced from the rear, and from which it projects axially toward the front; and in eliminating the projecting portion of the fiber by polishing, by means of an appropriate gauge.
This technique is not suitable when it is desired to maintain the stripped end of the fiber recessed by a certain distance from the front face of the end of the ferrule.
The applicant company has described, in its European Patent 0011561, a process for immobilizing an optical fiber in a connector ferrule with a slight recess with respect to the end, by breaking the optical fiber, which is carried out by making a scratch with an appropriate tool on the stripped end of the fiber, recessed from the end of the ferrule, and then applying axial traction to the fiber to divide it.
The technique described in this European patent is suitable for fibers comprising a casing or cladding that is relatively soft, insofar as it requires a slight compression of the casing, but is not directly usable for fibers having a hard casing.
This known technique, of dividing fibers by breaking them, is furthermore difficult to carry out in practice, because of the difficulty of precisely controlling the placement and depth of the scratch on the fiber, because of the substantial dimensions of the tool with respect to the dimensions of the ferrule and of the fiber.
The present invention is intended to provide a process by which an optical fiber can be mounted in a connector element, in such a way that its end is recessed by a predetermined distance from the end face of the ferrule, or in the plane of this end face, and in a particularly simple, rapid, and reliable manner.
The method according to the invention is characterized by the fact that after the end of an optical fiber has been stripped, the fiber is inserted from the rear in the connector element, in such a manner that it projects axially from the front end of the ferrule; the non-stripped end of the optical fiber is immobilized at the rear of the connector body; the axial position of the stripped part of the fiber, relative to the front face of the ferrule, is modified by a mechanical force applied to either the fiber or the ferrule; with the aid of an appropriate tool, positioned in a precise manner with respect to the plane of reference, a scratch is made in or in front of the plane of the front face of the ferrule; the fiber 10 is broken at the position of the scratch; and the fiber or the ferrule is allowed to return, or is elastically restored, to its initial position.
According to a first embodiment of the invention, using a connector element in which the ferrule is axially movable with respect to the body, against an elastic return member accommodated in the body, a gauge is engaged on the ferrule, preferably by turning the peripheral joining nut; the gauge having a central bore whose diameter corresponds to the exterior diameter of the ferrule; the gauge comprising a first end surface intended to come into contact against the surface of the connector element body which defines the plane of reference, and a second end surface, which is remote from the first surface by a distance which is less, by a predetermined value, than the distance on the connector element between the frontal face of the ferrule and the plane of reference; such that when the gauge is engaged, the ferrule is pushed back with respect to the body by said predetermined difference value; in this position, a scratch is produced on the fiber projecting from the gauge, along the second end surface thereof, by means of an appropriate tool; an axial traction is exerted on the fiber to break it at the position of this scratch; after which said gauge is withdrawn, the ferrule returning to its initial position under the action of the elastic support member, the end of the optical fiber then being recessed from the end of the ferrule by a distance corresponding to the predetermined difference value.
The connector element is then ready for use and it is only necessary to mount it in a corresponding joining element.
The connector element for carrying out this first embodiment is advantageously characterized by the fact that the ferrule has at its rear end an annular flange of greater diameter, whose frontal face is able to come into contact against an abutment surface formed by a hooked portion of the bore of the connector element body, under the action of an elastic member accommodated in the body, which is constituted, for example, by spring washers in axial contact against the rear face of said flange.
A second embodiment of the process according to the invention, which can be carried out with conventional connector elements in which the ferrule is fixed with respect to the body, is characterized by the fact that relative axial displacement of the stripped part of the fiber with respect to the frontal face of the ferrule can be obtained by exerting traction at the stripped end of the fiber so as to cause an elastic elongation thereof; and then breaking it by means of an appropriate tool, with respect to which the connector element has been precisely positioned; after which the fiber is allowed to return by its own elasticity into the ferrule, the end of the fiber then being located either in the plane of the frontal face of the ferrule, or recessed by a predetermined distance with respect to the plane. The final position of the fiber in the ferrule is determined by adjusting the axial traction force exerted on the end of the fiber, and the distance of the tool with respect to the reference plane of the connector element, as a function of the mechanical characteristics of the fiber, particularly its modulus of elasticity, and as a function of its diameter.
In these two embodiments, the optical fiber can be immobilized by its non-stripped part at the rear of the connector body by any appropriate means, for example by adhesion or mechanical clamping; for example by gripping it with a lock member comprising a split tubular clamping part with a tapered exterior surface, which cooperates with the surface of a tapered bore provided in the rear part of the body.